Furoquinoline Alkaloids: Insights into Chemistry, Occurrence, and Biological Properties

Root idioblasts reveal a specialized underground site for the storage of putative alkaloids in Rutaceae

Rutaceae plants are a rich source of alkaloids, but their cell-specific localization remains relatively unknown in the underground tissues, except for the acridone-containing idioblasts in Ruta graveolens roots. To fill this gap, we used broad taxonomic sampling to investigate both the microchemistry and the root structure of Rutaceae species. Utilizing both transmitted light and epifluorescence microscopy, we examined seven distinct Rutaceae species to determine if root idioblasts were present. For the microchemical analysis of the idioblasts contents, we employed Nile red staining and Dragendorff's test. All analyzed species presented root idioblasts with contents that are reactive with Dragendorff's reagent and Nile red, suggesting the presence of putative alkaloids and lipophilic environments, respectively. These idioblasts are typically found in the radicular cortex and can be easily observed under UV light due to their autofluorescent contents. We found that the occurrence of root idioblasts is a widely distributed condition in Rutaceae, showing for the first time both structural and microchemical analyses for broad taxonomic sampling. These cell types could play an important role in alkaloid metabolism in the underground tissues of plants in this family and offer an exciting opportunity for future investigations.

Alkaloids Isolated from Vepris glandulosa with Antidiabetic Properties: An In Vitro and In Silico Analysis

Diabetes is a major global health issue and as current treatments fail, the search for new antidiabetic drugs is crucial. This investigation, focusing on identifying potential antidiabetic compounds from the endangered plant species Vepris glandulosa, led to the isolation of two known alkaloids, choisyine acetate (1) and choisyine (2). The study established the in vitro inhibitory activities and in silico molecular interaction of the two alkaloids with α-amylase based on IC50 values, Linewaever-Burk/Dixon plot kinetic analyses and Molecular docking, respectively. The α-amylase inhibition assay revealed noncompetitive inhibition for both compounds with IC50 and Ki values of 4.74±0.17 and 4.75 mM for compound 1, and 11.29±0.44 and 12.37 mM for compound 2, respectively. In comparison, the standard drug acarbose displayed a competitive mode of inhibition, with IC50 and Ki values of 11.99±0.02 and 12.68 mM, respectively. The binding affinities with α-amylase were -6.42 and -6.07 kcal/mol for compounds 1 and 2, respectively relative to acarbose -8.03 Kcal/mol. Moreover, these two compounds' predicted physicochemical and ADMET properties justified their potential as lead compounds for drug discovery. These compounds demonstrated remarkable inhibition potential comparable to the standard drug, highlighting their potential as viable alternatives in managing diabetes.

Antibacterial and antioxidant potentials, detection of host origin compounds, and metabolic profiling of endophytic Bacillus spp. isolated from Rauvolfia serpentina (L.) Benth. ex Kurz

The research highlights the importance of exploring endophytic microbiomes of medicinal plants to uncover their potential for secondary metabolite production and their role in the biosynthesis of host-derived compounds. This study was aimed to isolate leaf endophytic bacteria of Rauvolfia serpentina, investigate their antibacterial, antioxidant potentials and detect host-origin compound reserpine using Reverse Phase High-Performance Liquid Chromatography (RPHPLC). Untargeted analysis via Ultra High-Performance Liquid Chromatography-High-Resolution Mass Spectrometry (UHPLC-HRMS/MS) was conducted for profiling main phytochemicals in the leaves and to explore potential bioactive compounds in bacterial extracts. Nine bacterial isolates were obtained from R. serpentina leaves. These isolates exhibited positive results in various biochemical tests including indole production, methyl red, Voges-Proskauer, citrate utilization, catalase and oxidase production, nitrate reduction, oxidative fermentation, and citrate reduction tests. Endophytic isolates RSLB3 and RSLB18 exhibited most potential antibacterial activity against tested human pathogenic bacteria and were identified as Bacillus sp. The extract of RSLB3 and RSLB18 also showed significant antioxidant activity compared to leaf extract. The total phenol content was similar in both these isolates while flavonoids content and DPPH scavenging activity was higher in isolate RSLB3. RPHPLC analysis confirmed the presence of reserpine in bacterial metabolites when compared to a standard reference. UHPLC-HRMS profiling unveiled a diverse range of host-derived compounds and reaction intermediates with known and unknown bioactive properties in leaf extract, RSLB3, and RSLB18. To our knowledge, this is the first study to achieve a comprehensive profiling.

Topical delivery of bioactive compounds from Cortex Dictamni alleviates atopic dermatitis-like lesion by inhibiting the activation of keratinocytes, macrophages, and basophils: Dictamnine versus fraxinellone

Dictamnine and fraxinellone constitute the primary alkaloid and limonoid components in Cortex Dictamni, respectively. Both compounds exhibit anti-inflammatory properties. This study aims to assess the ability of dictamnine and fraxinellone in treating atopic dermatitis (AD) through in silico-, cell-, and animal-based experiments. The effects of these compounds on the coordinated activation of keratinocytes, macrophages, and basophils in AD development were investigated. A dinitrochlorobenzene (DNCB)-sensitized AD model in mice was employed to examine the in vivo anti-AD effects. Dictamnine and fraxinellone effectively reduced the release of proinflammatory effectors, including interleukin (IL)-4, IL-13, chemokine (C-C motif) ligand (CCL)5, and CCL17, by suppressing extracellular signal-regulated kinase (ERK) signaling in activated keratinocytes. The conditioned medium from dictamnine-treated macrophages reduced signal transducer and activator of transcription (STAT)3 in keratinocytes by 39 %, indicating the inhibition of keratinocytes-immune cell interaction. Both compounds comparably suppressed RBL-2H3 cell degranulation by decreasing histamine production. In vitro permeation test (IVPT) demonstrated three-fold greater skin absorption of topically applied dictamnine than fraxinellone. The in silico molecular docking manifested a preferable ceramide interaction with dictamnine over fraxinellone. Topical application of dictamnine decreased the mouse skin lesion development and the overexpressed cytokines/chemokines. This attenuation is comparable to the activity of tacrolimus ointment, a standard clinical treatment. Histological analysis revealed that dictamnine inhibited epidermal proliferation, reducing thickness from 220 to 97 μm. However, dictamnine did not restore the barrier function, as evidenced by the results of filaggrin and loricrin expression and in vivo transepidermal water loss (TEWL). The findings suggest that topical dictamnine can be a promising agent for alleviating AD inflammation.

Optimization of the Production of Secondary Metabolites from Furanocoumarin and Furoquinoline Alkaloid Groups in In Vitro Ruta corsica Cultures Grown in Temporary Immersion Bioreactors

Ruta corsica is a rare and endemic plant native to Corsica. Due to its limited distribution and the priority to preserve natural sites, has been insufficiently studied. In vitro cultures provide an opportunity to research R. corsica under controlled conditions. In the present study, in vitro cultures of R. corsica were conducted in PlantformTM bioreactors. The study aimed to assess the effects of growth cycle length (5 and 6 weeks) and different concentrations of plant growth regulators (NAA and BAP) at 0.1/0.1, 0.1/0.5, 0.5/0.5, 0.5/1.0, and 1.0/1.0 mg/L on biomass growth and secondary metabolite accumulation. HPLC analysis identified compounds in the furanocoumarin and furoquinoline alkaloid groups, with furanocoumarins being the primary secondary metabolites (maximum total content: 1571.5 mg/100 g DW). Among them, xanthotoxin, psoralen, and bergapten were dominant, with maximum concentrations of 588.1, 426.6, and 325.2 mg/100 g DW, respectively. The maximum total content of furoquinoline alkaloids was 661 mg/100 g DW, with γ-fagarine as the primary metabolite, reaching 448 mg/100 g DW. The optimal conditions for secondary metabolite accumulation in R. corsica cultures were a 5-week growth cycle and the LS 0.1/0.1 medium variant.

Penifuranone A: A Novel Alkaloid from the Mangrove Endophytic Fungus Penicillium crustosum SCNU-F0006

One previously undescribed alkaloid, named penifuranone A (1), and three known compounds (2-4) were isolated from the mangrove endophytic fungus Penicillium crustosum SCNU-F0006. The structure of the new alkaloid (1) was elucidated based on extensive spectroscopic data analysis and single-crystal X-ray diffraction analysis. Four natural isolates and one new synthetic derivative of penifuranone A, compound 1a, were screened for their antimicrobial, antioxidant, and anti-inflammatory activities. Bioassays revealed that penifuranone A (1) exhibited strong anti-inflammatory activity in vitro by inhibiting nitric oxide (NO) production in lipopolysaccharide-activated RAW264.7 cells with an IC50 value of 42.2 μM. The docking study revealed that compound 1 exhibited an ideal fit within the active site of the murine inducible nitric oxide synthase (iNOS), establishing characteristic hydrogen bonds.

Phytochemical Profiling Studies of Alkaloids and Coumarins from the Australian Plant Geijera parviflora Lindl. (Rutaceae) and Their Anthelmintic and Antimicrobial Assessment

Phytochemical profiling followed by antimicrobial and anthelmintic activity evaluation of the Australian plant Geijera parviflora, known for its customary use in Indigenous Australian ceremonies and bush medicine, was performed. In the present study, seven previously reported compounds were isolated including auraptene, 6'-dehydromarmin, geiparvarin, marmin acetonide, flindersine, and two flindersine derivatives from the bark and leaves, together with a new compound, chlorogeiparvarin, formed as an artefact during the isolation procedure and isolated as a mixture with geiparvarin. Chemical profiling allowed for a qualitative and quantitative comparison of the compounds in the leaves, bark, flowers, and fruit of this plant. Subsequently, a subset of these compounds as well as crude extracts from the plant were evaluated for their antimicrobial and anthelmintic activities. Anthelmintic activity assays showed that two of the isolated compounds, auraptene and flindersine, as well as the dichloromethane and methanol crude extracts of G. parviflora, displayed significant activity against a parasitic nematode (Haemonchus contortus). This is the first report of the anthelmintic activity associated with these compounds and indicates the importance of such fundamental explorations for the discovery of bioactive phytochemicals for therapeutic application(s).

A Review of the Ethnobotanical Use, Chemistry and Pharmacological Activities of Constituents Derived from the Plant Genus Geijera (Rutaceae)

Geijera Schott is a plant genus of the Rutaceae Juss. (rue and citrus) family, comprising six species which are all native to Oceania. Of the plants belonging to this genus, the most significant species that has a customary use is Geijera parviflora, which was used by Indigenous Australians, primarily as a pain reliever. Herein, a comprehensive review of the literature published on the genus Geijera from 1930 to 2023 was conducted. This is the first review for this plant genus, and it highlights the chemical constituents reported to date, together with the range of pharmacological properties described from the various species and different parts of the plant. These properties include anti-inflammatory, anti-microbial, anti-parasitic, insect repellent, analgesic, neuroactive, and anti-cancer activities. Finally, a reflection on some of the important areas for future focused studies of this plant genus is provided.

Antifungal and Phytotoxic Activities of Isolated Compounds from Helietta parvifolia Stems

The identification of natural and environmentally friendly pesticides is a key area of interest for the agrochemical industry, with many potentially active compounds being sourced from numerous plant species. In this study, we report the bioassay-guided isolation and identification of phytotoxic and antifungal compounds from the ethyl acetate extract of Helietta parvifolia stems. We identified eight compounds, consisting of two coumarins and six alkaloids. Among these, a new alkaloid, 2-hydroxy-3,6,7-trimethoxyquinoline-4-carbaldehyde (6), was elucidated, along with seven known compounds. The phytotoxicity of purified compounds was evaluated, and chalepin (4) was active against Agrostis stolonifera at 1 mM with 50% inhibition of seed germination and it reduced Lemna pausicotata (duckweed) growth by 50% (IC50) at 168 μM. Additionally, we evaluated the antifungal activity against the fungal plant pathogen Colletotrichum fragariae using a thin-layer chromatography bioautography assay, which revealed that three isolated furoquinoline alkaloids (flindersiamine (3), kokusagenine (7), and maculine (8)) among the isolated compounds had the strongest inhibitory effects on the growth of C. fragariae at all tested concentrations. Our results indicate that these active natural compounds, i.e., (3), (4), (7), and (8), could be scaffolds for the production of more active pesticides with better physicochemical properties.